It has become a relatively common practice to generate chlorine, for use in swimming pools, spas, and other water treatment applications, by electrolysis of a solution containing a chlorine salt. In conventional practice, common salt (i.e., sodium chloride—NaCl) is dissolved in pool or spa water. Less commonly, other chlorine salts, such as potassium chloride (KCl) may also be used. An electrolysis cell, sometimes called a salt chlorine generator, or simply “salt generator,” is installed in series with a pump and filter in a main line water circulation loop and used to electrolyze pool water to generate free chlorine from the brine solution. The chlorine then reacts with and oxidizes biological and other contaminants in pool water. However, introduction of salt into pool or spa water can lead to more rapid corrosion of hardware and equipment installed in a vicinity of a pool or spa. In addition, byproducts of electrolysis reactions using NaCl include formation of sodium hydroxide and other undesirable chemicals. Since, in conventional practice, virtually all byproducts of an electrolysis reaction remain in circulating pool or spa water, it is necessary to neutralize or remove such byproducts to avoid exposing swimmers or bathers to irritating or unsafe levels of caustic sodium hydroxide or other undesirable chemicals.
In some pool, spa, hot tub, or similar water treatment applications, ozone from an ozone generator may be used to provide an oxidation potential for oxidation reactions with various contaminants. Ozone can provide a higher oxidation potential than chlorine and may thus be more effective against some biological, chemical, or other contaminants than chlorine alone. However, due to the higher reactivity and instability of ozone, ozone will generally provide less residual reactivity for reacting with contaminants that may be introduced into water after initial neutralization of contaminants by an initial higher level of ozone. Thus, for some applications, it may be desirable to make use of both ozone and chlorine, or another halogen, in order to obtain the separate benefits of each in treating water. Other halogens, e.g., bromine, may also be generated from their salts, e.g., NaBr, KBr, in a manner similar to that described above for chlorine. Moreover, there are also some beneficial synergistic effects, as well as other non-obvious effects, when ozone and chlorine or another halogen are used together in a water treatment system. Some of these effects may be exploited to reduce maintenance and operating costs for pools, spas, and other facilities with such water purification systems, and other effects must be addressed to prevent undesirable responses from redox control systems, as described later herein, when both ozone and chlorine are used in a given water treatment application.
It is thus one object of the instant invention to provide novel and unobvious methods and apparatus for combining use of chlorine and ozone in a water treatment system in ways that exploit separate and combined properties of ozone and chlorine or other halogens, and associated reaction byproducts, to obtain synergistic benefits relative to treatment and purification of water or other fluids. It is another object of the invention to provide control methods and control systems that maintain desirable levels of chlorine or other treatment chemicals in a presence of influences and effects of ozone on conventional control systems, especially those employing redox sensors. It is another object of the invention to provide methods and apparatus for configuring and operating separate and combined components of a water treatment system using one or more halogens and ozone such that reliability is enhanced and maintenance (e.g., removing deposits from, or replacing, electrolysis plates) is reduced.
Other objects of the invention will become clear upon a reading of the following specification.